This invention relates to soundproofing for insulating sound generating devices or parts of systems particularly vibrating conveyers with insulation elements that are bordered by an inner face in the direction of the sound source and by an outer face in the direction away from the sound source; and the insulation elements comprising layers of insulation material with a hollow cavity component. Such insulation is used for acoustic insulation and optionally also thermal insulation of equipment, installation parts, motors or machines, in particular for vibration conveyers. This invention preferably includes soundproofing that can be removed quickly by hand and reinstalled again in the event of inspections, repairs, problems, etc.
The known insulation systems have various disadvantages. The most common type of insulation is so-called cassette insulation, such as that described as thermal insulation in German Patent 36 36 341. However, cassettes of similar design are also widely used for soundproofing. A cassette is understood to be a housing made of steel plate or chrome steel plate with an open inside. To achieve a sound absorbing effect, insulation mats are inserted into the cassette from the inside. The surface of the insulation mats facing inward may be flat or may optionally have a three-dimensional structure. The air movements of the sound waves are hindered or attenuated in the insulation mat. If it is assumed that sound is reflected on the sheet metal wall of the cassette housing, the maximum air movements are at a distance of one-quarter wavelength from this reflective surface. To be able to optimally dampen these air movements, the thickness of the insulation mat would have to be in the range of one-quarter wavelength. With a justifiable layer thickness, this is possible only at a high frequency, because wavelengths in the low frequency range down to approx. 500 Hz are more than 60 cm, so the quarter wavelength would be more than 15 cm accordingly. At 2 kHz, the quarter wavelength is approx. 4 cm, which is thus within the range of the insulation material layer thicknesses conventionally used. Accordingly, the known soundproofing is effective only in the high frequency range with a frequency of more than 1 kHz.
If devices are enclosed in such cassettes, metallic housing side edges extend from the inside of the insulation to the outside in the contact area between adjacent cassettes or between a ring of cassettes and a cover element adjacent to this ring. Such housing side edges form sound bridges which greatly promote unwanted transmission of sound toward the outside. Accordingly, such a soundproofing system does not provide an adequate noise reduction effect even in the high frequency range.
The absorption coefficients of various materials and wall structures depend on the frequency. Essentially, fiber material has a high absorption coefficient in the range of 1 kHz. For example, measurements on a concrete wall coated with a fiber material have yielded absorption coefficients of 0.14, 0.20, 0.79 and 0.37 at frequencies of 125 Hz, 250 Hz, 1 kHz and 4 kHz. A plywood board has an elevated absorption coefficient in the low frequency range. Absorption coefficients of 0.60, 0.30, 0.09 and 0.09 have been determined for frequencies of 125 Hz, 250 Hz, 1 kHz and 4 kHz by performing measurements on a plywood board. The greater absorption in the low frequency range can be explained by resonance and the energy absorbing internal friction of the plywood board. The low absorption in the high frequency range shows that high frequency vibrations have little effect on friction because of the small amplitudes.
In addition to cassettes that are open toward the inside, cassettes which include a perforated plate as the inner face, so that a sheet metal face is adjacent to the soft insulation layer on both the inside and outside, are also used. In this way, absorption in the low frequency range should be combined with absorption provided by fiber mats in the high frequency range. Sound absorbing resonators are formed and kept open between the two metal plates due to the holes in the perforated plate arranged on the inside. The resonators and the insulation layer guarantee sound absorption in the respective frequency ranges according to the respective dimensions of the resonators and the absorption property of the insulation material. The cohesive area of the perforated plate arranged on the inside forms a reflective surface at least for the high frequency range. The sound component reflected on this reflective surface can excite resonance that is radiated outward over sound bridges, depending on the shape of the interior space adjacent to the insulation, for various frequency ranges.
The known soundproofing system for sheathing equipment usually guarantees a relevant sound absorbing effect only in certain portions of the high frequency range. However, since many types of equipment generate sound with frequency components in frequency ranges that are far apart, at least individual frequency components are not absorbed enough. In the case of equipment with very high sound levels, the ambient air quality standards or guideline values cannot be met with the known insulation, in particular when various types of such equipment are set up in one working area.
International Patent application WO 97/48943, a patent application by the present applicant, describes insulation which is in direct contact with the three-dimensional outside surface of structural components. It includes a contact layer or a friction layer made of sheet metal and/or wire mesh which is in contact with the structural component. To achieve stability of the insulation elements and to be able to absorb axial forces between adjacent insulation elements, solid supporting half-rings arranged on the end faces of the insulation elements are in contact with the structural component and extend over the entire thickness of the insulation element. These supporting half-rings or solid ribs form unwanted sound bridges which extend essentially over the entire thickness of the insulation elements and thus transmit sound from the interior of the insulation to the environment. Another disadvantage of the insulation according to International Patent WO 97/48943 is that it can only be mounted directly on the structural component, not at a desired distance from it. In addition, this insulation is designed mainly as thermal insulation and does not have the desired damping properties over the entire frequency range.
Vibrating conveyers or so-called vibrators that transmit vibrations have the object of supplying components that are used in an automatic assembly operation, such that they are supplied serially and in particular in the proper cycle. To do so, these vibrators are in the form of a vessel with a curved bottom and a conical side wall. At least one spiral-shaped ramp is provided on the conicalside wall. Vibration of the vessel is induced by magnet-metal spring packages which are arranged between the vessel and a solid base. Because of this vibration, the loose parts accommodated in the vessel are moved toward the wall of the vessel and on the ramp toward the output end of the ramp. The noise emitted by the vibrators has two different sources. First, a low frequency hum, the so-called transformer hum, is emitted by the magnet-metal spring packages. The sound level of this low frequency component is very high. For example, a sound pressure level of 90 dB(A) has been measured at 16 Hz. On the other hand, the moving loose parts produce noise in the high frequency range. This noise is formed by relative movement between the loose parts and the vibrating vessel or ramp and by collisions between abutting parts of the loose parts. There are also parts with a natural resonance that can be excited by the vibration. Other noise sources include blast nozzles or deflection devices which are optionally present and guarantee for example a desired conveyance of the isolated loose parts.
Depending on the loose parts fed in the individual case, noise levels of more than 100 dB may occur with vibrators; this is hazardous for the health of the operating personnel and also reduces productivity. Known vibrator sound reduction measures include, for example, two insulation cassettes in the form of half rings with a sheet metal housing that is open toward the inside and a 30 mm thick nubby foam layer of polyurethane. These two cassettes are joined in the form of a ring around the vibrator. They must not be in contact with the vibrator, because otherwise the vibrator movements would be disturbed. A 5 mm thick plexiglass cover is placed on the flange or the upper end edge of the housing. The supply and separation of parts in the vibrator can be monitored visually by operating personnel through the plexiglass cover. The separated loose parts then pass out of the interior of the insulation to a processing station through an outlet opening. It has now been found that a maximum total sound reduction of only 10 dB(A) can be achieved with such a soundproofing system. Therefore, in the case of a vibrator with a high sound level, the sound level of the insulated vibrator is even above the maximum continuous sound pressure level of 85 dB(A) which can be tolerated for industrial activities. The sound reduction effect in the low frequency range or damping of transformer hum in particular is very weak. The large sound component in the environment is transmitted outward as airborne noise and as structure-borne noise.
The object of the present invention is to provide an insulation which greatly reduces both airborne noise and structure-borne noise transmission. On the whole, a significantly greater reduction in the total sound level is to be achieved in comparison with the known soundproofing systems. In particular, a reduction in the total audible frequency range is to be achieved, i.e., in both the low frequency range and the high frequency range, so that this soundproofing system can be used in a variety of ways.
This object is achieved through the features of claim 1. The dependent claims describe alternative and advantageous embodiments.
In achieving this object, it has been found that all possible sound suppression measures must be as completely effective as possible, independent of one another. A broadband absorption spectrum is achieved with a textile sound absorbing membrane which is preferably made at least partially of synthetic threads, in particular glass fiber threads and/or wire. The textile sound absorbing membrane is preferably designed as a woven fabric, but optionally as a braided or knit fabric, a wire mesh or wire screen. Thus, this is a textile surface or a textile material. However, multidirectional wire layers or optionally thread layers that are bonded together but not woven may also be used as the sound absorbing membrane. The sound absorbing membrane preferably has a high density and is optionally coated. This increases the inertia of the sound absorbing membrane, so that it makes the desired inelastic soundproofing feasible in the low frequency range. It is self-evident that the inertia of the sound absorbing membrane can be optimized according to the respective application or the effective frequency spectrum by adapting the cross section, density and material of the thread and/or the wire, but a standard design of the sound absorbing membrane is usually sufficient. A sound absorbing membrane designed like a woven fabric makes it possible to achieve a mechanical friction between sections of thread or wire that are in contact with one another in addition to internal friction within the threads or wires. This friction guarantees a high sound absorbing capacity of the resonant sound absorbing membrane.
Because of its textile structure, the sound absorbing membrane does not have any large partial areas with a smooth surface to function as a reflective surface. The textile structure like that of a woven fabric preferably has a high density of through-holes, so that this structure is permeable for the high frequency range. The high frequency range is absorbed strongly in the soft insulation material after passing through the sound absorbing membrane. The insulation material consists of a long-fiber layer material, preferably silicate fiber mats, and it has cohesive air channel systems for absorption of high frequency sound. In the passage of the high frequency sound component through the membrane, in particular resonating with a low frequency component, a diffraction occurs at the through-holes through the fabric membrane, increasing the sound absorbing effect. The high density of extremely small through-holes permits movement of air relative to the skin, which has a strong friction effect. This prevents a purely elastic resonance of the sound absorbing membrane. These through-holes through the membrane are not to be understood as inlet openings of discrete resonators as is the case with perforated plates. Therefore, the absorption is also not limited to a narrow frequency range.
A wire cloth in particular can be used as the sound absorbing membrane, preferably using chromium wire or a high-grade steel wire for use at high temperatures or in the possible presence of moisture. If a sound absorbing membrane is not exposed to high temperatures, it may optionally be made of synthetic fibers, but preferably glass fibers or ceramic fibers, optionally with wires braided into them. The density (mass per unit of area), the air permeability, the oscillational, frictional and soundproofing properties are optimized so that the desired noise reduction effect is achieved. A wire mesh that was used has 130 mesh/cm2 and an open area in the range of 40-55%, e.g., approx. 51%. The weight of this wire cloth is approx. 0.910 kg/m2 with a wire diameter of approx. 0.25 mm. Since the effect of this coarse wire mesh is very weak, microfilter metal cloth has also been used.
Microfilter metal cloth has a very high mesh count per area plus optionally special weave structures and is formed from wire having a small cross section. Accordingly, a filter fineness of a few micronsxe2x80x94e.g., 20 xcex7mxe2x80x94and a small air passage cross section or air permeability value can be achieved. The wires of the flat microfilter material preferably have diameters in the range of 0.02 mm to 0.4 mm, in particular 0.04 mm to 0.13 mm and the mesh count in one direction is in the range of 80 to 1000 per cm. A conventional commercial microfilter metal cloth with a warp wire diameter of 0.042 mm and a weft wire diameter of 0.125 mm has a mesh count of 600xc3x97125 per cm2. This filter cloth has a weight of approx. 0.850 kg/m2, which essentially corresponds to the weight of the wire cloth mentioned above. In addition to the difference in air permeability, another difference between these two types of wire cloth given as examples is their mobility. The cloth made of thicker wires has a much greater resistance to bending, which has a negative effect on the resonance in the short wavelength or high frequency sound range. Since the microfilter metal cloth has a much greater wire diameter in the weft direction than in the warp direction, it has a much greater resistance to bending in the weft direction than in the warp direction. When using warp and weft wires of different thicknesses, an optimal resistance to bending which has a sound absorbing effect can be achieved with microfilter metal cloth in at least one direction.
However, if the development of turbulence at the through-holes and/or the weight per unit of area and/or the friction in the vibrating membraneis to be increased in order to achieve an optimized absorption of sound in the low frequency range, then only the inner face or outer face or optionally another membrane, in particular an interlayer between the inner and outer faces may be provided with a different air permeability and/or a greater weight per unit of area and/or a greater frictional effect or uptake of energy of deformation.
The combination of the sound absorbing membrane with the soft insulation material also has the advantage that the low frequency movement of the sound absorbing membrane is retarded not only by internal friction and by the mechanical friction in the fabric but also by the deformation of the insulation material which has a frictional effect because of the sound absorbing membrane moving against it. The insulation material then assumes the function of at least partially inelastic resiliency of the sound absorbing membrane when compressed. These frictional and sound absorbing effects permit a broadband inelastic sound absorbing effect with the help of the sound absorbing membrane in the area of the inner face of an insulation element.
The stable flat material provides at least an essentially smooth reflective surface which reduces the escape of sound on the one hand while influencing the inner sound field on the other hand so that the node faces of the reflected sound develop on this reflective surface. This also increases the sound absorbing effect of the insulation material adjacent to the reflective surface in the direction of the inner face, because this insulation material is thus not in the area of node faces. The stable flat material is optionally produced from metal in one layer, in particular with the metal layer having a thickness of at least 1.5 mm, but optionally from at least two layers of metal and rubber or a rubbery material, in particular with a rubber layer facing the inner face.
It is self-evident that the stable flat material can be brought to the desired shape by bending or pressing, but optionally also by casting or extruding, in which case plastics and rubber may optionally also be used in addition to metallic materials. The stable flat material guarantees dimensional stability to the insulation elements which is not based on supporting rings but instead is based on a stable or fixedly shaped cylindrical surface. This makes it possible to prevent sound bridges, and at least one reflective surface, which is important for the sound absorbing effect, is provided. Insulation elements with a layer of stable flat material may be designed to be free-standing or mounted on the structural component. In the case of mounting on the structural component, the shape of the stable flat material must be adapted to the shape of the structural component. To do so, the layers of the insulation elements must be produced from blanks that guarantee contact of the insulation elements with the structural component. The use of such blanks is known from International Patent WO 97/48943. The content of International Patent WO 97/48943 is also to be included in the disclosure content of the present invention, and is hereby incorporated herein by reference in its entirety and for all purposes.
The insulation element according to this invention guarantees the optimal effect of the three elements at the same time, namely the sound absorbing membrane, the insulation material and at least one reflective surface. However, not only is the overall effect to be understood as obtained by superimposing the individual effects, but instead an effect which goes beyond the sum of the individual effects can be achieved through the proposed arrangement of the three elements and the design of the sound absorbing membrane described here.
To be able to join the insulation elements together easily and in a soundproof manner, they include at least two covering skins, preferably made of fiberglass fabric. An inner skin of the covering facing the sound source thus forms a sound absorbing membrane. Optionally, however, an additional sound absorbing membrane, preferably a wire cloth, is arranged on the inner skin of the covering facing the sound source. A covering outer skin is provided in the area of the outer face. The two covering skins are joined together to form a closed covering. First, velcro strips and tabs with matching second velcro strips are attached to the covering outer skins, so that adjacent insulation elements can be secured to one another tightly by means of these velcro-type fasteners. To prevent outlet gaps or openings from developing, the velcro fasteners preferably extend along the entire contact areas between the insulation elements to be joined. Velcro fasteners are optionally also provided on the contact areas that come in contact on the lateral end faces.
In the case of vibrators or other devices, it is expedient to mount the vibrator or other device on a foam layer at the bottom. At least two insulation elements which also rest on the foam layer should be joined together in a ring around the vibrator or the device to form a closed jacket. On the upper end face, this jacket is connected to at least one other ring-shaped or partially ring-shaped closure insulation element. By connecting the coverings with velcro fasteners, tight but not rigid connections without sound bridges are formed. To nevertheless be able to monitor the vibrator visually despite the soundproofing, an inspection port is preferably provided together with a cover in these closure insulation elements. The cover includes two transparent plates arranged with a space between them.